Organogenesis

Embryonic Development

The development of the muscular system begins around the fourth week of gestation in humans.

Fetal Development

Muscle tissue is formed in the mesoderm layer of the embryo in response to signals from fibroblast growth factor, serum response factor, and calcium.

In the presence of fibroblast growth factor, myoblasts fuse into multi-nucleated mytotubes, which form the basis of muscle tissue.
These myoblasts then undergo a process called myogenesis, where they fuse together to form multinucleated muscle fibers. As development progresses, muscle fibers continue to grow and mature.

Unused myoblasts dedifferentiate into myosatellite cells, which remain in the muscle fiber until needed to differentiate into new muscle cells when a muscle is damaged or stressed.

Myocytes are tubular muscle cells or fibers that develop from myoblasts.
Myocytes are specialized as cardiac, skeletal, or smooth muscle cells.

All skeletal and cardiac muscles and most smooth muscles arise from mesoderm cells, except the pupillary muscles which arise from ectoderm.